In Hamkingdom, Prince Bo is telling the tale of the Ham-Ham Games, an event which occurs only once every 8686 years in Hamcropolis, to the Rainbow Girls, a team of cheerleaders. He tells them about the Everlasting Torch, a fiery symbol of friendship. A team of runners gets to take the torch up to Hamcropolis and start the Ham-Ham Games! The Rainbow Girls happily volunteer to take the torch themselves. Prince Bo, however, has already chosen the Ham-Hams to do it. The Rainbow Girls are upset, and they think that no one could possibly do it better than them, so Ivy, Rosie, and Daisy, the Rainbow Girls, decide to steal the torch from the Ham-Hams and take it to Hamcropolis.
Meanwhile, the Ham-Hams are enjoying a lazy summer day, when Hamtaro spots a "shooting star" and all the Ham-Hams chase after it. When it lands, it turns out that it is not a star, but an umbrella with a note attached. It says that they are chosen to take the torch up to Hamcropolis! Elder Ham happens to be there and he explains about the Ham-Ham Games and Hamcropolis. They search for the torch until a flash of rainbow lights the umbrella with a rainbow fire and it becomes the torch. Stan starts to show off and sprains his paw, so Panda agrees to stay behind with him. Elder Ham also stays and watches Snoozer, while eating a seed roasted from a fire created by the torch.
The Ham-Hams decide to take turns running with the torch so that they won't become tired. They sing a song to keep up their spirits on the way, accompanied by an instrumental version of the new theme song. They all get tired anyway and then the Rainbow Girls arrive and swipe the torch. They introduce themselves and get disgusted when the ham-hams ask if they're supposed to know them. As they argue amongst each other about what the purpose of the torch is, Hamtaro swipes it back and tells them exactly what it's for. The ham-hams give the Rainbow Girls the shake and head on their way, but it doesn't work for long.
Prince Bo finds Elder Ham munching on his seed. Noticing that the ham-hams are gone, he explains that he had a job for the Rainbow Girls, but they didn't listen and ran off. He then notes the fire and Snoozer mumbles in his sleep that it was lit from the Everlasting Flame. Prince Bo uses the flame to like a lantern as a backup, just in case something should happen to the Everlasting Flame. He declines Elder Ham's offer to share some of the giant seed and heads on his way.
Back on the trial, the Rainbow Girls fly and attack and the ham-hams are forced to scramble. Boss holds them off while Hamtaro and Oxnard escape with the torch. They soon fall off a cliff, but a boat of pirate hamsters show up before they land in the water. It turns out that the boat is manned by two members of one of the teams, the Sea Hams. All of a sudden, the flying ship begins to tip over. They soon diagnose the problem: The engine's fire is out. If they don't re-light it soon, the ship will go down, taking the hamsters and the torch with it! At that moment, the Rainbow Girls appear once again. Hearing that Hamtaro is planning to use the torch to light the engine, they tell him that there's no way they're letting him use it instead of a match. They don't care if the ship goes down: they have wings. They try to grab it away, but Hamtaro evades him and lights up the engine. The flame has more power that first thought, and the Rainbow Girls disappear once again, and Hamtaro and Oxnard fall out of the boat and onto an unknown island.
They land and find some ham-hams arguing over the torch. The hamsters are inhabitants of Junglebell Island, and they wear costumes to make themselves bigger, for they are much smaller than other hamsters. They are also training for the Ham-Ham Games, but they are too nervous to try. Realizing that Hamtaro is the torch-bearer, they give it back to him. Just then, the Rainbow Girls show up in a rowboat. They found the other hamsters and chased them all around their training field, hurdling, pole jumping, and running on the race track. They challenged Hamtaro and Oxnard to a race. For a while, Hamtaro and Oxnard get caught up in it, but then the Jungle Hams direct Hamtaro and Oxnard to sneak off into some bushes. The Rainbow Girls win the race, but find that it got them nothing.
A sound is heard: the ham-hams have arrived with Sabu on birds to save them! Hamtaro shares the flame with the Jungle Hams to encourage them in their training. The Rainbow Girls use their wings and fly up to the birds and begin a scramble to get the torch. A storm hits, and everyone flies right into it! Hamtaro falls out of the sky and lands in the middle of the desert into a sand storm. The torch is going out, and as Hamtaro goes to save it, he sees the Rainbow Girls stuck in the sand. They tell him to save the torch, but he decides to save them first. They may not be friends as such, but they're fellow ham-hams. The torch has gone out, and the Rainbow Girls are angry, and upset that they've let down Prince Bo.
The ham-hams arrive and they're all upset about the torch too. They finally decide that there's nothing they can do about it and start talking about what tell Prince Bo. Suddenly, he arrives. The Rainbow Girls all run up and apologize for letting them down, and he explains to them about the job he had wanted them to do. He has the backup torch with him --- but it turns out it's gone out too! Everyone is now in complete dismay: It looks like the Ham-Ham Games will have to wait 8686 more years. But then, the birds, Sabu, Jingle, Herbert, the Sea Hams and the Jungle Hams arrive. They all had a part of the torch to carry. They thought Hamtaro might be in trouble, so they all decided to return the favors he had done for them by bringing the flame. Hamtaro lights his torch, and Prince Bo reveals Hamcropolis to them. He makes a rainbow that leads to Hamcropolis. Everyone runs up the rainbow to watch Hamtaro light the torch on Hamcropolis, which makes for a very happy ending. Hamtaro, however, is left wondering if anyone wants a used umbrella.